The present invention relates to a motion-adaptive scanning-line conversion circuit for converting at least part (M) of a first video signal having a first number (N) of scanning lines into a second video signal having a second number (L) of scanning lines. The video signal may be a television signal.
The conversion may be from part only (M&lt;N) of the first number of the scanning lines to the second number (L), and the second number (L) may be larger than the first number (N). For instance, N=480, M=360 and L=720 or 1080. This may be the case where the letter-box type NTSC signals having 480 effective scanning lines of which 360 lines are in the main part and 120 lines are in the upper and lower mask parts are converted for display on a wide vision receiver having 720 scanning lines or HDTV receiver having 1035 effective scanning lines.
The conversion may be from part only (M&lt;N) of the first number of the scanning lines to the second number (L), and the second number (L) may be equal to the first number (N). For instance, N=L=480, and M=360. This may be the case where the letter-box type NTSC signals having 480 effective scanning lines of which 360 lines are in the main part and 120 lines are in the upper and lower mask parts are converted for display on a wide vision receiver having 480 effective scanning lines.
The conversion may be from the entirety (M=N) of the first number of the scanning lines to the second number (L), and the second number (L) may be larger than the first number (N). For instance, N=N=480, and L=960. This may be the case where the full-mode NTSC signals having 480 effective scanning lines are converted for display on a wide vision receiver having 960 scanning lines.
Where the video signals are of the letter-box type, with high-precision information added in the upper and lower mask parts, a high-precision information conversion filter may be additionally provided to demodulate the high-precision information and add it to the video signals transmitted in the main part of the letter-box type signals.
In this case, the conversion is from part only (M&lt;N) of the first number of the scanning lines to the second number (L), and the second number (L) may be larger than the first number (N), or may alternatively be equal to the first number (N). In an example of the former case, N=480, M=360 and L=720 or 1080. In an example of the latter case, N=L=480 and M=360.
FIG. 35A and FIG. 35B show an example of conventional scanning-line conversion. FIG. 35A shows an example of input signal, which has an aspect ratio of 4 to 3 and has 525 scanning lines per frame, like a television signal of the NTSC system. Of the 525 scanning lines, 480 scanning lines are effective scanning lines, and 360 scanning lines are used for expressing a picture actually displayed on the screen. FIG. 35B shows an example of output signal having an aspect ratio of 16 to 9. In the conventional scanning-line conversion, the vertical deflection is controlled such that the number of-the scanning lines of the display is 360, as illustrated in FIG. 35B.
FIG. 36 shows a circuit for the vertical deflection used for the conversion of the scanning lines shown in FIG. 35B. In the example shown in FIG. 36, a CRT is used for display. A vertical deflection circuit 431 generates a deflection current of the saw-tooth waveform, shown in FIG. 37B, in which the horizontal axis represents the time and the vertical axis represents the magnitude of the current. A deflection coil 432 is excited by the current from the vertical deflection circuit 431, and generate a magnetic field which deflects the electron beam in the CRT 433.
For performing the display shown in FIG. 35B, the electron beam is deflected over the entire height of the screen while it is horizontally scanned for 180 lines, so that interlaced scanning with 360 lines per frame is achieved.
By comparing FIG. 37B with FIG. 37A, which shows the saw-tooth waveform used for deflecting the electron beam over the entire height of the screen while the electron beam is horizontally scanned for 240 lines (with the number of the effective scanning lines being 480), it will be observed that the amplitude of the saw-tooth wave is larger In FIG. 37B: That is, during the raster scanning, it starts with a higher level and falls with a steeper gradient, to a lower level. During the flyback period, it rises from the lower level to the higher level.
The width or amplitude of the vertical deflection during each field is therefore larger, and the number off scanning lines formed within-the screen (used for display of the picture) is less. A result is-that the coarseness of the scanning lines is prominent.
Another problem associated with the conventional motion-adaptive processing in which stationary picture processing and moving picture processing are motion-adaptively, after having converting the video signal of the interlaced scanning into the video signal of the progressive scanning, is that the difference in the quality of the picture obtained by the stationary picture processing and the picture obtained by the moving picture processing, and the degradation in the picture quality during the moving picture processing is prominent. Moreover, the memory used for the inter-frame or inter-field processing must have a large capacity, so the device is expensive.
Another example of a conventional scanning-line conversion is shown in FIG. 38A, FIG. 38B, FIG. 39, and FIG. 40. FIG. 38A shows an example of input signal of the letter box type. In the television signal of the NTSC system, the wide aspect ratio (e.g., 16 to 9) is compressed in the vertical direction, and is disposed in the central part of the screen with the aspect ratio of 4 to 3. The upper and lower mask parts of the screen is used to transmit enhancing signals such as vertical high-frequency component. The effective scanning lines per frame (which has 525 scanning lines) is 480, of which the video signal is expressed in 360 scanning lines. The enhancing signals may comprise a vertical frequency component of 180/2 to 360/2 cph with the horizontal frequency of not higher than about 1.4 MHz. FIG. 38A shows an example of output signal. It shows how the image signal of FIG. 38A is displayed on the display of the aspect ratio of 16 to 9. In the conventional scanning-line conversion, the enhancing signals in the upper and lower mask parts are demodulated, and used for the scanning-line conversion to produce 480 display scanning lines as shown in FIG. 38B.
FIG. 39 shows an example of conventional scanning-line conversion circuit. It comprises input terminals 461 and 462, an output terminal 463, time-base conversion memories 464, 471 and 472 for performing time-base conversion, a high-precision information demodulating circuit 465 For demodulating the high-precision information multiplexed in the upper and lower mask parts, an intra-field scanning-line interpolating circuit 466 for producing interpolated scanning line by intra-field arithmetic operation, an inter-field scanning-line interpolating circuit 467 for producing interpolated scanning line by inter-field arithmetic operation, a motion detecting circuit 468 for detecting motion by calculating the inter-frame difference, an adder 469, a mixer 470 for mixing the two input signals with a mixing ratio dependent on the control signal, and an intra-field conversion filter 473 for performing the scanning-line conversion by vertical filtering of the pixels within the same field.
The operation will next be described. Digital video signals are input to the input terminals 461 and 462. The video signal input to the input terminal 461 is written into the time-base conversion memory 464, and the high-precision information multiplexed in the upper and lower mask parts is read and is subjected to time-base conversion. The high-precision information in the upper and lower mask parts is also rearranged into the required number of the scanning lines. The video signal input to the input terminal 462 is input to the high-precision information demodulating circuit 465, the intra-field scanning-line interpolating circuit 466, the inter-field scanning-line interpolating circuit 467, the motion detecting circuit 468 and the time-base conversion memory 471.
The output of the memory 464 having been time-base converted, is input to the high-precision information demodulating circuit 465. In the high-precision information demodulating circuit 465, the high-precision information multiplexed in the upper and lower mask parts is demodulated by calculation on the output of the time-base conversion memory 464 and the signal input to the input terminal 462, into a component having a vertical frequency of about 180/2 to 360/2 cph and having a frequency not higher than about 1.4 MHz. The output of the high-precision information demodulating circuit 465 is supplied to the adder 169.
The intra-field scanning-line interpolating circuit 466 generates interpolated scanning lines by calculation on the pixels with the same field. The inter-field scanning-line interpolating circuit 467 generates interpolated scanning lines by calculation on pixels separated by one field. The output of the intra-field scanning-line interpolating circuit 466 is supplied to the adder 469. The output of the inter-field scanning-line interpolating circuit 467 is supplied to the mixer 470. The motion detecting circuit 468 detects motion of the image on the basis of the inter-frame difference.
The adder 469 adds the output of the high-precision information demodulating circuit 465 and the output of the intra-field scanning-line interpolating circuit 466. The output of the high-precision information demodulating circuit 465 is the vertical high-frequency component obtained by demodulating the high-precision information that was multiplexed in the upper and lower mask parts, and has a vertical frequency of 360/2 to 180/2 cph and a horizontal frequency of not higher than about 1.4 MHz. By adding this output of the high-precision information demodulating circuit 465 and the output of the intra-field scanning-line interpolating circuit 466, which is not higher than 180/2 cph, the vertical frequency band of the interpolated scanning line is expanded to 360/2 cph.
The motion detection circuit 468 detects the motion of the image. More specifically, it determines, for each pixel, whether the pixel is in a moving part of the picture on the basis of the video signals separated by one frame. The output of the motion detecting circuit 468 is input to the mixer 470. The mixer 470 mixes the output of the adder 469 and the output of the inter-field scanning-line interpolating circuit 467 in accordance with the result of the motion detection from the motion detection circuit 468. When the motion detection circuit 468 finds that the pixel is in a moving part of the picture, the output of the intra-field scanning-line interpolating circuit 466 is selected, while when the pixel is found to be in a stationary part of the picture, the output of the inter-field scanning-line interpolating circuit 467 is selected. The output of the mixer 470 is input to the time-base conversion memory 472.
The time-base conversion memory 471 is for performing time-base conversion of the real scanning lines. The time-base conversion memory 472 is for performing time-base conversion of the interpolated scanning lines. The time-base conversion memories 471 and 472 read the signals of the 360 scanning lines of the main image part for a period of 480 scanning lines. The output of the time-base conversion memories 471 and 472 are input to the intra-field conversion filter 473. The intra-field conversion circuit 473 converts the number of the scanning line by vertical filtering of the pixels in the same field. The output of the intra-field conversion filter 473 is output via the output terminal 463.
FIG. 40 shows the manner of scanning line conversion in which 480 scanning lines are generated from 360 scanning lines. For this to be achieved, four scanning lines are generated from every three scanning lines. Each of the four scanning lines are formed by weighted average of straight-line interpolation of the original three lines.
In the above arrangement, the interlaced scanning is converted to the progressive scanning and the scanning-line conversion is then performed by the motion adaptive processing. The system is associated with tile same problems that were described in connection with the first-mentioned prior art. That is, the difference in picture quality between moving picture processing and stationary picture processing is prominent. Although the use of the high-precision information alleviates the problem to some extent, it does not completely solve the problem. This is particularly true where the bandwidth of the high-precision information is not sufficient. In addition, there is an additional problem that the volume of the circuit is large.